Help with 7536A-1 and a 8 pin IC with no numbers

I am trying to replace some pieces in a circuit that produces police siren sounds and cant find new ones. one i believe is a transistor with the numbers 7536a-1 and an 8 pin IC with no numbers on it. Can someone please help me identify these. I am new to electronics and not real familiar with a lot of these items.

Staff: Mentor

I am trying to replace some pieces in a circuit that produces police siren sounds and cant find new ones. one i believe is a transistor with the numbers 7536a-1 and an 8 pin IC with no numbers on it. Can someone please help me identify these. I am new to electronics and not real familiar with a lot of these items.

Welcome to the PF. Can you try to google for info about the circuit board itself? Does it have a name on it, or other numbers that might help to identify it? If you can get a schematic off the web, that will help you a lot in trying to do any component replacements. Especially if one IC has been black-topped (painted to conceal the original identifying info).

There are no numbers on the ic chip itself, nor are there any numbers on the board. If any one can tell me how to post a pic of the board i will do that. it consist of the ic chip whick has 8 pins another 3 pin that looks like a transistor and has the numbers 7536A-1 on it. then it has 3 caps, one 100uf and 2 104 disk caps and that is it.

Staff: Mentor

The little black-topped chip might be a simple microcontroller. In which case, you'd need the program inside the uC in order to duplicate it. If the developer was smart, they used "Secure" at the end of programming their uC, so that others could not easily reverse-engineer their work.

Which brings up the question -- why are you trying to duplicate this board?

Staff: Mentor

No just repair it. i think i burnt up the ic, not really sure all i know is it wont work anymore. i have already replaced the parts i know only thing left to replace is the 2 parts i mentioned.

Where did you get it from originally? If that's a black-topped uC, you probably won't be able to fix it.

BTW -- have you tried beeping out the "transistor" to see if it's okay or blown? Have you tried drawing a schematic from the PCB itself? That might ttell you more about the circuit (like, what type of transistor it is).

Staff: Mentor

the numbers on the three leg transistor show 7536A-1 but i cant find any info on this anywhere

Does your DVM have a "diode test" setting on it? If so, try beeping the trransistor out to figure out if it is an NPN or PNP. Worst case you can unsolder it from the PCB to get full access to the pins without other circuitry hooked onto them (which can confuse your diode test beeping).

If your DVM doesn't have a diode test setting, you can generally still use a simple resistance measurement instead. Measure between each set of 2 pins, checking both polarities.

The siren does 4 different tones, if I cant find a way to fix this one is it possible to build a very simple circuit that will do the same thing. not real good with electronics but am willing to give it a try if someone can help i wopuld appreciate it.

Staff: Mentor

Looks a lot like what you are describing -- an 8-pin DIP IC and a TO-92 transistor, with a couple of discretes. If you can read the writing on top of the IC (I'm not able to), that might give you one of your answers.

Maybe see if there is kit information for that board, if it looks similar to yours. Might be based on the same root design.

This is a bit of a guess, but does the IC have the power going to two pins that are diagonally opposite each other in two of the corners? These would have a track going between them on the printed circuit board. Or, at least, does the + supply go to pin 8?
And does it have pin 1 going to the negative supply? This is unusual among chips.

The most likely chip someone would use in a siren could be a 555.
see this site:
http://www.uoguelph.ca/~antoon/gadgets/555/555.html [Broken]
No siren there, but info on 555 chips.

It is very common for producers of circuits to grind the numbers off so nobody can easily copy the circuit.

Testing the transistor is easier. If you have a digital multimeter look for a diode mode. Test the pins of the transistor (in circuit for a start) for conduction one way but not the other. One of the pins, (the base) should conduct to both other pins in one direction but not the other.
If any of the pins conduct very well in both directions, the transistor may be faulty and should be tested again out of circuit.
Testing in OHMS mode usually will not work because the meter tests at a low voltage which won't turn the diode junction on.
Exact replacement of the transitor probably isn't necessary and anything NPN would be worth a try.

If you are going to replace the two most expensive things on the board, maybe you should just rebuild the whole thing from new parts?

i want to thank everyone for the help. I cant find my exact siren but i have found a few kits online that i can just buy and replace mine. again thanks for all the help. if i find out anything about this circuit i will post and let you know.

only 5 of the 8 pins appear to be used, 3 of them are not even soldered in. Pins 1,3 and 4 are not even used. pin 2 goes to a wire on the switch, pin 5 goes to ground, pin 6 goes to a speaker wire, pin 7 runs through the positive side of the 2 caps and one of the outer pins on the transistor i beleive it is the c pin, pin 8 hooks to the other speaker wire. if this helps please let me know